1. Field of the Invention
This invention concerns large, lightweight, inflatable structures such as satellite decoys and ship decoys. More particularly, this invention relates to inflatable tubes used as supports in such structures.
2. Description of the Prior Art
Large, lightweight, inflatable structures find various applications. Generally speaking, these devices need structural members as reinforcement. Conventional ship decoys or satellite decoys are large, inflatable structures which typically employ internal inflatable tube frames for structural support.
The sizing of the tubes in such a tube frame is determined, at least in part, by the cross sectional area moment of inertia. In other words, a tube size is conventionally chosen to prevent the tubes from buckling and thereby keeping the decoy from collapsing under its own weight.
With a large cross section, a tube in a tube frame requires a large gas volume to inflate. Using tubes, particularly with a large cross section, also increases the weight of the entire decoy due to the weight of material required to construct the inflatable device and the gas required for inflation.
A typical satellite decoy is fabricated and packaged in a canister along with gas required to inflate the decoy. The decoy is packaged in a canister to conserve space on the launch vehicle for other cargo. For the satellite decoy, the weight and volume of the deflated satellite decoy as well as the weight and volume of inflation gas are crucial in reducing launch costs.
Advances in inflatable devices have enabled easier inflation of devices such as air-mattresses or tents, but at the expense of added material weight. For instance, U.S. Pat. No. 4,065,888 issued to Napierski, incorporated herein by reference, describes an inflatable device which reduces the effort required to pump up the device. The Napierski device uses two air inlet valves, valves a, and b. Valve a is used to blow up an outer shell, tube frame or skeleton which requires a relatively limited air volume to give structure to the overall device. Upon inflation through valve a, air is simultaneously drawn through valve b to fill the remainder of the inflatable device which has a much larger air volume. Thus, a reduced effort is required to complete pumping the inflatable tube through valve b. FIGS. 6 and 7 of Napierski show a tent with inflatable support props which require a relatively large air volume to inflate, however, by using inflatable skeletons inflated by separate valves, pump-up time for the full support prop is reduced.
Advances have also been made in manufacturing techniques for inflatable devices. U.S. Pat. No. 3,742,658 issued to Meyer, incorporated herein by reference, shows a geodesic structure which is formed by sealing two sheets of flexible material together with the sealing lines disposed in a triangular pattern to form a series of inflatable tubes. Excess edge material is severed away from the edges of the flexible material, and the edges are then joined to complete the inflatable geodesic structure. Meyer refers to the tubular edges as edge struts.